1. Field of the Invention
The present invention relates to an energy-trap type piezoelectric resonator, and more particularly to a piezoelectric resonator which effectively utilizes the resonance characteristics based on desired vibration while suppressing the generation of unwanted vibration that produces spurious responses.
2. Description of the Related Art
Conventionally, an energy-trap type piezoelectric resonator has been widely used in piezoelectric oscillators and other devices. In this kind of piezoelectric resonator, since vibration other than the desired vibrational mode produces spurious responses, it is essential to suppress the generation of unwanted vibration.
Conventional devices have attempted to damp unwanted vibration. For example, Japanese Unexamined Utility Model Publication No. 4-119123 discloses an energy-trap type piezoelectric resonator including damping materials provided in island elements at the end portions of a piezoelectric substrate, adjacent to a resonance section.
Also, Japanese Unexamined Utility Model Publication No. 3-79528 discloses a load capacitor incorporating piezoelectric oscillator shown in FIG. 13. A piezoelectric oscillator 51 includes a piezoelectric resonator 52, and a capacitor 53 for providing a load capacitor. The piezoelectric resonator 52 is constructed of a piezoelectric substrate 54 with a rectangular plate shape. At the central portions of both main surfaces of the piezoelectric substrate 54, excitation electrodes 55 are arranged to be opposed to each other via the piezoelectric substrate 54. This section including the excitation electrodes 55 opposed to each other via the substrate on the top and bottom surfaces constitutes an energy-trap type resonance section. A damping electrode 56 is located above this resonance section in the vicinity of a side surface 54a of the piezoelectric substrate 54. By providing soldering on the damping electrode 56, unwanted vibration is damped.
In an energy-trap type resonator, the relationship between the resonance section and the damping material is very important. That is, if the position of the damping material is improper, the desired main vibration is damped, or the damping of unwanted vibration is not achieved.
In the conventional art disclosed in Japanese Unexamined Utility Model Publication No. 4-119123, a damping material is disposed only at the end portion of the piezoelectric substrate at a specified distance from the resonance section of the piezoelectric substrate, but it is very difficult to accurately position such a damping material. This conventional piezoelectric resonator, therefore, is very difficult to produce, experiences failures due to the misalignment of damping material. Also, the damping material disposed in island elements causes another problem in that cracks are often produced in the piezoelectric substrate when applying the damping material or on the processing line thereafter. In addition, the difficulty in accurately disposing the damping material makes it difficult to reduce the size of the piezoelectric resonator.
In the piezoelectric oscillator disclosed in the Japanese Unexamined Utility Model Publication No. 3-79528, the damping electrode 56 provided on the piezoelectric substrate 54 is very small. Therefore, it is difficult to apply solder on the damping electrode 56. To accurately apply the solder, it is necessary to enlarge the area of the electrode for damping 56, which also makes size-reduction of the piezoelectric resonator 52 difficult.
To overcome the above-described problems, preferred embodiments of the present invention provide a much smaller and easily produced energy-trap type piezoelectric resonator, which effectively damps unwanted vibration and utilizes intended vibration, and which facilitates external electrical connections.
The piezoelectric resonator in accordance with preferred embodiments of the present invention includes a piezoelectric substrate, first and second excitation electrodes partially provided on the first and second main surfaces of the piezoelectric substrate, respectively, and opposed to each other via the first and second excitation electrodes on the top and bottom surfaces, first and second lead-out electrodes electrically connected to the first and second excitation electrodes, respectively, and provided on the first and second main surfaces of the piezoelectric substrate, respectively, and first and second terminal electrodes for establishing external connections with the outside provided at the end portions of the respective first and second lead-out electrodes, the end portions being opposed to the sides where the respective first and second excitation electrodes are connected. At least one of the first and second terminal electrodes has an electrode extension portion arranged to extend into the imaginary region where the first and second excitation electrodes are extended to at least one of the side edges of the piezoelectric substrate.
Preferably, the mean normal-line distance from the outer peripheral edge of the excitation electrode to the inside edge of the electrode extension portion is at least about 1.2d, where d is the diameter of the excitation electrode.
More preferably, soldering is provided on the electrode extension portion. In this case, soldering is provided over the entire upper surfaces of the terminal electrodes.
The piezoelectric resonator in accordance with preferred embodiments of the present invention also may preferably include first and second lead terminals soldered to the respective first and second terminal electrodes by soldering, thereby providing a piezoelectric resonator with leads.
Other features, elements, steps, characteristics and advantage of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.